Recently, there has been an increasing thrust in the application of internal antennas in wireless communications devices. The concept of an internal antenna stems from the avoidance of using an external radiating element through the integration of the antenna into the communications device itself. Internal antennas have several advantageous features such as being less prone to external damage, a reduction in overall size of the communications device with optimization, and easy portability. In most internal antennas, the printed circuit board of the communications device serves as the ground plane of the internal antenna.
Current antenna solutions for Multiple Input Multiple Output (MIMO) applications require multiple antennas. While multiple antennas provide numerous benefits, they present numerous design challenges, as well. One such challenge is mutual coupling between the antennas, which can result in wasted power when transmitting and a lower received power from incoming signals. In MIMO technologies such as Long Term Evolution (LTE), where two receive antennas are required, cross-coupling effects can be highly undesirable since effective MIMO performance requires relatively low correlation between each of the received signals of the multiple antennas. When multiple antennas are used within a mobile handheld device, the signals received by each of the antennas may be undesirably correlated, due to the tight confines typical of the compact devices that are favored by consumers. This can considerably affect MIMO performance. Accordingly, minimal coupling between antennas in MIMO antenna arrays is preferred to increase system efficiency and battery life, and thereby improve received signal quality. In order to optimize the characteristics of MIMO antenna arrays, a significant level of testing is generally required.